Abstract

Coda Q, or Qc, is determined from the rate of coda decay in the Coastal Plain near Charleston, South Carolina. The mean of Qc calculated from individual estmates is near 190 at 1 Hz and increases to over 1650 at 10 Hz. A possible temporal change in Qc is identified, high values being associated with increased seismic activity during late 1977. Temporal changes have been observed elsewhere and laboratory measurements of Q under different stress states correlate high Q with high stress. A spatial variation in Qc is identified, increasing from west (Qc at 10 Hz equal to 850) to east (Qc at 10 Hz greater than 2100) across the Coastal Plain. The demarcation of high to highest zones of Qc is coincident with the western boundary of the innermost isoseismal of the Charleston 1886 earthquake. It is hypothesized that the 1886 earthquake was mislocated originally because of this spatial variation in energy attenuation that was unrecognized at that time.

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